The present invention concerns a hydraulic system for selectively loading a hydraulic pump to absorb driveline energy of a vehicle to brake same. The broad concept of utilizing hydraulic pumps and the like to absorb energy from a vehicle driveline is well known as evidenced by U.S. Pat. No. 3,759,355 granted to the present inventor with other hydraulic braking systems being disclosed in U.S. Pat. Nos. 2,905,276; 3,185,261; and 3,593,828.
The systems disclosed in the earlier patents are not intended for use with pump means now often included as a standard transmission component in certain types of heavy duty trucks. Normally such power take-off pumps are in splined engagement with a truck transmission component and are used for powering hydraulic components such as, for example, the hydraulic rams of a truck having a tiltable dump body.
A further disadvantage to known systems is the lack of back up safety provisions and limited driver control of the system. Driver control is limited, for the most part, to either an "on" or "off" condition of the energy absorbing system.